1. Field of the Invention
The present invention relates to a manufacturing method of an optical waveguide which is widely used for optical communications, optical information processing and other general optics.
2. Description of the Related Art
Optical waveguides typically include a core provided in a predetermined pattern as a light passage on a surface of an under-cladding layer, and an over-cladding layer covering the core. The core has a higher refractive index than the under-cladding layer and the over-cladding layer adjoining the core for prevention of leak of light passing through the core. As differences in refractive index between the core and the cladding layers increase, the light passing through the core becomes less liable to leak, leading to higher light transmission efficiency. For production of such an optical waveguide, a method employing a photolithography process (see, for example, Japanese Patent Application Laid-Open No. 2007-11067) and a method employing a photo-bleaching process (see, for example, Japanese Patent Application Laid-Open No. 2006-299066) have been proposed.
In an optical waveguide manufacturing method employing the photolithography process, photosensitive resins each having a known refractive index (which is not changed by exposure) are used as materials for the under-cladding layer, the core and the over-cladding layer for setting the differences in refractive index. For the formation of the predetermined core pattern, a core formation photosensitive resin layer formed on the surface of the under-cladding layer is exposed via a photomask formed with an opening pattern conformal to the core pattern, and then developed with a developing solution. Thus, an unexposed portion is dissolved away, and an exposed portion remains as having the predetermined pattern.
In an optical waveguide manufacturing method employing the photo-bleaching process, a single photo-bleaching material is partly exposed for the core formation so as to provide a difference in refractive index between an exposed portion and an unexposed portion (the exposed portion has a reduced refractive index). The unexposed portion, which has a higher refractive index than the exposed portion, serves as the core having the predetermined pattern.